"The crew is safe and under the circumstances in good spirits," the company said in a statement. "The well-being of the crew remains our paramount concern."

Maersk said that according to its information, the ship was being escorted towards Bandar Abbas in Iran by Iranian patrol boats.

The U.S. Navy has dispatched a guided-missile destroyer, the USS Farragut, and three patrol boats to the southern end of the Persian Gulf.

The Tigris is being held in Iranian territorial waters, and it is unclear what circumstances would trigger a response or whether the U.S. is willing to engage militarily with the Iranians.

Col. Steve Warren, a Pentagon spokesman, said the United States “has the discretion to take action” under maritime law. He said that would require a presidential order.

The takeover of the Tigris was the second incident of Iranian “harassment” of free shipping within the Strait of Hormuz in four days, Warren said. On April 24, four Iranian Revolutionary Guard gunboats “harassed” the American-flagged cargo ship Maersk Kensington as it transited the Strait into the Persian Gulf.